1. Field of the Invention
The present invention relates to semiconductor wafer processing systems and, more particularly, to a conductive, vacuum tight feed-through that extends from one side of a dielectric body to another while maintaining a difference in pressure from one side of the body to the other.
2. Description of the Background Art
A semiconductor wafer processing system typically contains a process chamber within which a semiconductor wafer is processed. In a physical vapor deposition system, the interior of the process chamber is maintained at a specific temperature and pressure while a process gas is introduced into the chamber. The process gas is energized to form ions that impact a target such that target material is sputtered and deposited on the wafer.
The wafer is supported in the chamber by a pedestal, where the pedestal contains various components that provide heating and cooling of the wafer, as well as wafer clamping (chucking) to maintain the wafer in a stationary position during processing. Wafer retention is typically performed using an electrostatic chuck, which uses electrostatic force to retain the wafer upon the pedestal.
Generally, semiconductor wafer processing requires a gas pressure within the chamber that is different from atmospheric pressure. This different pressure is maintained in the process chamber above the pedestal and forms a process environment for the wafer. Due to the various components found within and below the pedestal, it is necessary to maintain atmospheric pressure (or some other pressure that is different from the pressure for the process environment) in a volume within the pedestal. Thus, the pedestal itself separates two volumes which are at different pressures. A detailed description of such a pedestal is described in a commonly assigned U.S. patent application Ser. No. 08/567,625, filed Dec. 5, 1995, and incorporated herein by reference.
In an electrostatic chuck, the pedestal requires one or more conductive feed-through connectors to provide a conductive path from one side of the pedestal to the other, e.g., from the low pressure volume to the high pressure volume. As such, in addition to coupling electrical signals through the chuck, it is also necessary for these feed-throughs to preserve the pressure difference found on either side of the pedestal, i.e., they must be vacuum sealed. One type of electrostatic chuck disclosed in commonly assigned U.S. patent application Ser. No. 08/873,268 filed Jun. 11, 1997, and hereby incorporated by reference, teaches the need for a conductive path to the surface of the chuck to provide wafer detection sensors. This specific embodiment avoided using a conductive feedthrough within the chuck itself by applying current to the gas feed through tubing. Commonly assigned U.S. patent application Ser. No. 08/834,702 filed Apr. 1, 1997 discloses feed-through construction for coupling voltage to electrodes embedded in the chuck using solid pins. The solid pin electrically contacts certain conductive layers embedded within the pedestal body.
However, there are disadvantages to using solid conductive pins. First of all, finish machining is necessary when a flatness requirement is imposed on the solid pin (i.e., when the pin must be flush with the surface of the pedestal). Finish machining involves a risk of contaminating or damaging the chuck surface material. If finish machining is to be avoided, extremely tight tolerances are necessary in the conducting pin and the joining of the pin to the pedestal. Second, stress in the ceramic body resulting from the mismatch in thermal coefficients of expansion between ceramic and metal can cause cracking in the ceramic and destroy the vacuum integrity of this joint.
Therefore, there is need in the art for a conductive feed-through that preserves the pressure difference without requiring the use of a solid conducting pin, as well as a method for fabricating such a feed-through.